Although many of the transport characteristics of urinary acidification have been extensively examined, little is known about the energetics of H ion transport. This proposal is concerned with the examination of the energy-substrate requirement of H ion transport in an in vitro urinary membrane, the bladder of the fresh water turtle. This preparation provides the opportunity to examine simultaneously the metabolic function of the epithelium and its capacity to transport H ion. Previous studies have demonstrated that in this epithelium H ion transport has a marked O2 dependence, a preference for the substrate glucose and the transport rate is coupled linearly to metabolism. The turtle bladder metabolism via the pentose shunt varies with the rate of H ion transport. Therefore, it is proposed that H ion transport is primarily dependent on pentose shunt metabolism and that NADPH, generated by the pathway, is the substrate utilized for the process of H ion transport. To further evaluate this proposal the following will be examined: 1. the stoichiometric relationship between the rate of H ion transport and glucose metabolism by the pentose shunt; 2. the distribution of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in the different cells of this epithelium and the effect of inhibitors of these enzymes on H ion transport; 3. the role of NADP/NADPH ratio and NADPH depletion in the control of pentose shunt metabolism and H ion transport; 4. the effect of hormones, such as adlosterone that increase H ion transport, on the enzymes of the pentose shunt and on the pathways of glucose metabolism; and 5. the presence of mucosal membrane dehydrogenases that utilize NADPH as substrate. From these studies a basic understanding of the metabolic requirement and regulation of H ion transport can be obtained. These concepts can then be extended where appropriate to clinical disorders of urinary acidification.